Millimeter-wave links are of a line-of-sight nature. Hence, multiple-input multiple-output (MIMO) systems operating in the millimeter-wave band may not achieve full spatial diversity or multiplexing.
Millimeter-wave (mmWave) technology operating at frequencies in the 30 GHz and 300 GHz range is considered as a potential solution for 5th generation (5G) wireless communication systems to support multiple gigabit per second wireless links. The large communication bandwidth at mmWave frequencies will enable mmWave systems to support higher data rates compared to microwave-band wireless systems that have access to very limited bandwidth. However, significant pathloss and hardware limitations are major obstacles to the deployment of mm-wave systems.
In order to combat their relatively high pathloss compared to systems at lower frequencies and the additional losses due to rain and oxygen absorption, mmWave systems require a large directional gain and line-of-sight (LoS) links. This large directional gain can be achieved by beamforming, using either a large antenna array or a single reconfigurable antenna element, which has the capability of forming its beam electronically. Such reconfigurable antennas are available for commercial applications.
As an example, composite right-left handed (CRLH) leaky-wave antennas (LWAs) are a family of reconfigurable antennas with those characteristics. By employing reconfigurable antenna elements where each antenna is capable of configuring its radiation pattern independent of the other antennas in the array, a LoS millimeter-wave multiple-input multiple-output (MIMO) system can achieve both multiplexing and diversity gains. The former will result in better utilization of the bandwidth in this band, while the latter can allow designers to overcome the severe pathloss.
Although the advantages of reconfigurable antennas are well-documented, the space coding designs for MIMO systems are mostly considered based on the assumption that the antenna arrays at the transmitter and the receiver are omnidirectional (i.e., there is no control mechanism over the signal propagation from each antenna element). Deploying reconfigurable antennas in MIMO arrays can add multiple degrees of freedom to the system that can be exploited to design new space coding designs that improve the system performance compared to existing schemes.
In recent years, several block-coding techniques have been designed to improve the performance of MIMO systems employing reconfigurable antennas. There is a coding scheme that can increase the diversity order of conventional MIMO systems by the number of the reconfigurable states at the receiver antenna. The technique has been extended to MIMO systems with reconfigurable antenna elements at both the transmitter and receiver sides, where a state-switching transmission scheme is used to further utilize the available diversity in the system over flat fading wireless channels. However, using such coding schemes, the system is only able to transmit one symbol per channel use (i.e., they do not provide any multiplexing gain). Moreover, the detection complexity of the codes in such schemes is high, and increases with the number reconfigurable states at the antenna.
What is needed is a coding scheme (e.g., a predesigned manipulation of the transmitted signal) for MIMO systems that can transmit multiple symbols per channel.
This “Discussion of the Background” section is provided for background information only. The statements in this “Discussion of the Background” are not an admission that the subject matter disclosed in this “Discussion of the Background” section constitutes prior art to the present disclosure, and no part of this “Discussion of the Background” section may be used as an admission that any part of this application, including this “Discussion of the Background” section, constitutes prior art to the present disclosure.